1. Field of the Invention
The present invention relates to an opto-electric hybrid board in which an electric circuit board with an optical element mounted thereon and an optical waveguide are stacked together.
2. Description of the Related Art
With the increase in the amount of transmission information, optical interconnection in addition to electrical interconnection has been used in recent electronic devices and the like. As an example of such a technique, an opto-electric hybrid board has been disclosed in Japanese Published Patent Application No. 2009-288341. As shown in FIG. 7, this opto-electric hybrid board includes: an electric circuit board E0 including an insulative layer 51, and electrical interconnect lines 52 formed on the front surface of the insulative layer 51; an optical waveguide (optical interconnect lines) W0 (including an under cladding layer 56, cores 57 and an over cladding layer 58) stacked on the back surface (a surface opposite from the surface with the electrical interconnect lines 52 formed thereon) of the insulative layer 51 of the electric circuit board E0; and a light-emitting element 11 and a light-receiving element 12 which are mounted on portions of the surface with the electrical interconnect lines 52 formed thereon, the portions corresponding to opposite end portions of the optical waveguide W0. The opposite end portions of the optical waveguide W0 are formed into inclined surfaces inclined at 45 degrees with respect to the electric circuit board E0. Portions of each of the cores 57 positioned at the inclined surfaces function as first and second light reflecting surfaces 57a. Portions of the insulative layer 51 corresponding to the light-emitting element 11 and the light-receiving element 12 have first and second through holes 55, respectively, for an optical path. The first and second through holes 55 allow a light beam L to propagate therethrough between the light-emitting element 11 and the first light reflecting surface 57a provided in a first end portion of the optical waveguide W0 and between the light-receiving element 12 and the second light reflecting surface 57a provided in a second end portion thereof.
The propagation of the light beam L in the aforementioned opto-electric hybrid board is performed in a manner to be described below. First, the light beam L is emitted from the light-emitting element 11 toward the first light reflecting surface 57a. The light beam L passes through the first through hole 55 for an optical path formed in the insulative layer 51, and then passes through the under cladding layer 56 in the first end portion (the left-hand end portion as seen in FIG. 7) of the optical waveguide W0. Then, the light beam L is reflected from the first light reflecting surface 57a of each of the cores 57 (or the optical path is changed by 90 degrees), and travels through the interior of each core 57 in an axial direction. Then, the light beam L is reflected from the second light reflecting surface 57a provided in the second end portion (the right-hand end portion as seen in FIG. 7) of each core 57 (or the optical path is changed by 90 degrees), and travels toward the light-receiving element 12. Subsequently, the light beam L passes through the under cladding layer 56 in the second end portion, and travels outwardly of the optical waveguide W0. Then, the light beam L passes through the second through hole 55 for an optical path, and is received by the light-receiving element 12.
However, the light beam L is diffused as shown in FIG. 7 when emitted from the light-emitting element 11 and when reflected from the second light reflecting surface 57a. Thus, the light beam L is low in the efficiency of propagation. To solve such a problem, Japanese Published Patent Application No. 2002-258081, for example, discloses a technique in which a lens 60 is mounted to an opening surface of the second through hole 55 for an optical path to change the light beam L passing through the second through hole 55 into a collimated light beam or a convergent light beam by the effect of the lens 60, as shown in FIG. 8. This technique changes the light beam L into a collimated light beam or a convergent light beam as mentioned above to achieve the efficient propagation of the light beam L.
However, the lens 60, which is mounted, involves the need for the step of mounting the lens 60, resulting in a problem such that the productivity is lowered. The process of mounting the lens 60 also results in a problem such that variations occur in the accuracy of the position of the mounting.
In view of the foregoing, an opto-electric hybrid board is provided which includes a lens formed in an optical path between an optical element and a core with stable positional accuracy without the decrease in productivity.